Inhibitory effect of alpha-lipoic acid and its positively charged amide analogue on nitric oxide production in RAW 264.7 macrophages

Lipoic Acid and Fish Oil Combination Potentiates Neuroinflammation and Oxidative Stress Regulation and Prevents Cognitive Decline of Rats After Sepsis

Sepsis causes organ dysfunction due to an infection, and it may impact the central nervous system. Neuroinflammation and oxidative stress are related to brain dysfunction after sepsis. Both processes affect microglia activation, neurotrophin production, and long-term cognition. Fish oil (FO) is an anti-inflammatory compound, and lipoic acid (LA) is a universal antioxidant substance. They exert neuroprotective roles when administered alone. We aimed at determining the effect of FO+LA combination on microglia activation and brain dysfunction after sepsis. Microglia cells from neonatal pups were co-treated with lipopolysaccharide (LPS) and FO or LA, alone or combined, for 24 h. Cytokine levels were measured. Wistar rats were subjected to sepsis by cecal ligation and perforation (CLP) and treated orally with FO, LA, or FO+LA. At 24 h after surgery, the hippocampus, prefrontal cortex, and total cortex were obtained and assayed for levels of cytokines, myeloperoxidase (MPO) activity, protein carbonyls, superoxide dismutase (SOD), and catalase (CAT) activity. At 10 days after surgery, brain-derived neurotrophic factor (BDNF) levels were determined and behavioral tests were performed. The combination diminished in vitro levels of pro-inflammatory cytokines. The combination reduced TNF-α in the cortex, IL-1β in the prefrontal cortex, as well as MPO activity, and decreased protein carbonyls formation in all structures. The combination enhanced catalase activity in the prefrontal cortex and hippocampus, elevated BDNF levels in all structures, and prevented behavioral impairment. In summary, the combination was effective in preventing cognitive damage by reducing neuroinflammation and oxidative stress and increasing BDNF levels.

Alpha-lipoic acid effects on brain glial functions accompanying double-stranded RNA antiviral and inflammatory signaling

Double-stranded RNAs (dsRNA) serve as viral ligands that trigger innate immunity in astrocytes and microglial, as mediated through Toll-like receptor 3 (TLR3) and dsRNA-dependent protein kinase (PKR). Beneficial transient TLR3 and PKR anti-viral signaling can become deleterious when events devolve into inflammation and cytotoxicity. Viral products in the brain cause glial cell dysfunction, and are a putative etiologic factor in neuropsychiatric disorders, notably schizophrenia, bipolar disorder, Parkinson's, and autism spectrum. Alpha-lipoic acid (LA) has been proposed as a possible therapeutic neuroprotectant. The objective of this study was to test our hypothesis that LA can control untoward antiviral mechanisms associated with neural dysfunction. Utilizing rat brain glial cultures (91% astrocytes:9% microglia) treated with PKR- and TLR3-ligand/viral mimetic dsRNA, polyinosinic-polycytidylic acid (polyI:C), we report in vitro glial antiviral signaling and LA reduction of the effects of this signaling. LA blunted the dsRNA-stimulated expression of IFNα/β-inducible genes Mx1, PKR, and TLR3. And in polyI:C treated cells, LA promoted gene expression of rate-limiting steps that benefit healthy neural redox status in glutamateric systems. To this end, LA decreased dsRNA-induced inflammatory signaling by downregulating IL-1β, IL-6, TNFα, iNOS, and CAT2 transcripts. In the presence of polyI:C, LA prevented cultured glial cytotoxicity which was correlated with increased expression of factors known to cooperatively control glutamate/cystine/glutathione redox cycling, namely glutamate uptake transporter GLAST/EAAT1, γ-glutamyl cysteine ligase catalytic and regulatory subunits, and IL-10. Glutamate exporting transporter subunits 4F2hc and xCT were downregulated by LA in dsRNA-stimulated glia. l-Glutamate net uptake was inhibited by dsRNA, and this was relieved by LA. Glutathione synthetase mRNA levels were unchanged by dsRNA or LA. This study demonstrates the protective effects of LA in astroglial/microglial cultures, and suggests the potential for LA efficacy in virus-induced CNS pathologies, with the caveat that antiviral benefits are concomitantly blunted. It is concluded that LA averts key aspects of TLR3- and PKR-provoked glial dysfunction, and provides rationale for exploring LA in whole animal and human clinical studies to blunt or avert neuropsychiatric disorders.

Micronutrient modulation of NF-κB in oral keratinocytes exposed to periodontal bacteria

Chronic periodontal diseases are characterised by a dysregulated and exaggerated inflammatory/immune response to plaque bacteria. We have demonstrated previously that oral keratinocytes up-regulate key molecular markers of inflammation, including NF-κB and cytokine signalling, when exposed to the periodontal bacteria Porphyromonas gingivalis and Fusobacterium nucleatum in vitro. The purpose of the current study was to investigate whether α-lipoic acid was able to abrogate bacterially-induced pro-inflammatory changes in the H400 oral epithelial cell line. Initial studies indicated that α-lipoic acid supplementation (1-4 mM) significantly reduced cell attachment; lower concentrations (<0.5 mM) enabled >85% cell adhesion at 24 h. While a pro-inflammatory response, demonstrable by NF-κB translocation, gene expression and protein production was evident in H400 cells following exposure to P. gingivalis and F. nucleatum, pre-incubation of cells with 0.5 mM α-lipoic acid modulated this response. α-Lipoic acid pre-treatment significantly decreased levels of bacterially-induced NF-κB activation and IL-8 protein production, and differentially modulated transcript levels for IL-8, IL-1β, TNF-α and GM-CSF, TLR2, 4, 9, S100A8, S100A9, lysyl oxidase, NF-κB1, HMOX, and SOD2. Overall, the data indicate that α-lipoic acid exerts an anti-inflammatory effect on oral epithelial cells exposed to periodontal bacteria and thus may provide a novel adjunctive treatment for periodontal diseases.

Inhibitory effect of α-lipoic acid on platelet aggregation is mediated by PPARs

Peroxisome proliferator-activated receptors (PPARs) isoforms (α, β/δ, and γ are present in human platelets, and activation of PPARs inhibits platelet aggregation. α-Lipoic acid (ALA), occurring naturally in human food, has been reported to exhibit an antiplatelet activity. However, the mechanisms underlying ALA-mediated inhibition of platelet aggregation remain unknown. The aim of this study was to investigate whether the antiplatelet activity of ALA is mediated by PPARs. ALA itself significantly induced PPARα/γ activation in platelets and increased intracellular amounts of PPARα/γ by blocking PPARα/γ secretion from arachidonic acid (AA)-activated platelets. Moreover, ALA significantly inhibited AA-induced platelet aggregation, Ca(2+) mobilization, and cyclooxygenase-1 (COX-1) activity, but increased cyclic AMP production in rabbit washed platelets. Importantly, ALA also enhanced interaction of PPARα/γ with protein kinase Cα (PKCα) and COX-1 accompanied by an inhibition of PKCα activity in resting and AA-activated platelets. However, the above effects of ALA on platelets were markedly reversed by simultaneous addition of selective PPARα antagonist (GW6471) or PPARγ antagonist (GW9662). Taken together, the present study provides a novel mechanism by which ALA inhibition of platelet aggregation is mediated by PPARα/γ-dependent processes, which involve interaction with PKCα and COX-1, increase of cyclic AMP formation, and inhibition of intracellular Ca(2+) mobilization.

Antiplatelet activity of alpha-lipoic acid

Alpha-lipoic acid (ALA) is often used as a dietary supplement to prevent and treat chronic diseases associated with excessive oxidative stress. The aim of this study was to investigate the mechanisms of the antiplatelet activity of ALA. ALA significantly inhibited collagen-induced platelet aggregation, thromboxane B(2) (TXB(2)) formation, Ca(2+) mobilization, and protein kinase Calpha (PKCalpha) activation, but ALA itself increased cyclic AMP formation in rabbit washed platelets. However, the effects of ALA on the above platelet responses were markedly reversed by the addition of 2'5'-ddAdo, an adenylate cyclase inhibitor. Additionally, increased reactive oxygen species (ROS) formation and cyclooxygenase-1 activity stimulated by arachidonic acid were inhibited by ALA. In conclusion, we demonstrated that ALA possesses an antiplatelet activity, which may be associated with an elevation of cyclic AMP formation, involving subsequent inhibition of TXA(2), Ca(2+) mobilization, and PKCalpha-mediated pathways. Moreover, inhibition of ROS formation and increase of platelet membrane fluidity may also involve its actions.

Nitric oxide as a target of complementary and alternative medicines to prevent and treat inflammation and cancer

Nitric oxide (NO) and associated reactive nitrogen species (RNS) are involved in many physiological functions. There has been an ongoing debate to whether RNS can inhibit or perpetuate chronic inflammation and associated carcinogenesis. Although the final outcome depends on the genetic make-up of its target, the surrounding microenvironment, the activity and localization of nitric oxide synthase (NOS) isoforms, and overall levels of NO/RNS, evidence is accumulating that in general, RNS drive inflammation and cancers associated with inflammation. To this end, many complementary and alternative medicines (CAMs) that work in chemoprevention associated with chronic inflammation, are inhibitors of excessive NO observed in inflammatory conditions. Here, we review recent literature outlining a role of NO/RNS in chronic inflammation and cancer, and point toward NO as one of several targets for the success of CAMs in treating chronic inflammation and cancer associated with this inflammation.

Protective effect of lipoic acid on oxidative and peroxidative damage in cyclosporine A-induced renal toxicity

Free radical generation, including reactive nitrogen and reactive oxygen species, is known to participate in cell physiology in both a positive and negative manner. Moreover, alterations in their concentrations are implicated in a number of renal diseases. However, there is evidence that high concentration of nitric oxide (NO) occurring as a result of iNOS induction and peroxynitrite formation, is capable of causing lipid peroxidation and protein oxidation in cyclosporine A (CsA) induced cellular damage. The present study was conducted to investigate the possible protective role of Lipoic acid (LA) in nitric oxide mediated cellular abnormalities induced by CsA in rat kidney. Adult male albino rats of Wistar strain were given CsA at a dose of 25 mg/kg body weight, orally for 21 days. An extensive elevation in the activities of xanthine oxidase was noted in the renal tissue of the CsA administered rats. These changes were associated with significant increase in the levels of plasma lipid peroxidation with high protein carbonyl contents and 3-nitrotyrosine formation coupled with diminished protein thiols. In addition, plasma nitrite/nitrate (NO(x)), RT-PCR for inducible NOS (iNOS) mRNA, and immunohistochemically demonstrable iNOS protein were evaluated to assess peroxidative damage. Concomitant treatment with LA (20 mg/kg body weight, orally for 21 days showed that the oxidative stress alteration were significantly decreased in CsA treated renal tissue. While the expression of iNOS and the amounts of NO(x) were decreased simultaneously. These results indicate that the antioxidant LA might have a protective effect against CsA-induced peroxidative changes and cellular damage of the renal tissue of the rat.

The Effects and Mechanisms of Mitochondrial Nutrient α-Lipoic Acid on Improving Age-Associated Mitochondrial and Cognitive Dysfunction: An Overview

We have identified a group of nutrients that can directly or indirectly protect mitochondria from oxidative damage and improve mitochondrial function and named them "mitochondrial nutrients". The direct protection includes preventing the generation of oxidants, scavenging free radicals or inhibiting oxidant reactivity, and elevating cofactors of defective mitochondrial enzymes with increased Michaelis-Menten constant to stimulate enzyme activity, and also protect enzymes from further oxidation, and the indirect protection includes repairing oxidative damage by enhancing antioxidant defense systems either through activation of phase 2 enzymes or through increase in mitochondrial biogenesis. In this review, we take alpha-lipoic acid (LA) as an example of mitochondrial nutrients by summarizing the protective effects and possible mechanisms of LA and its derivatives on age-associated cognitive and mitochondrial dysfunction of the brain. LA and its derivatives improve the age-associated decline of memory, improve mitochondrial structure and function, inhibit the age-associated increase of oxidative damage, elevate the levels of antioxidants, and restore the activity of key enzymes. In addition, co-administration of LA with other mitochondrial nutrients, such as acetyl-L: -carnitine and coenzyme Q10, appears more effective in improving cognitive dysfunction and reducing oxidative mitochondrial dysfunction. Therefore, administrating mitochondrial nutrients, such as LA and its derivatives in combination with other mitochondrial nutrients to aged people and patients suffering from neurodegenerative diseases, may be an effective strategy for improving mitochondrial and cognitive dysfunction.

Dihydrolipoic acid inhibits skin tumor promotion through anti-inflammation and anti-oxidation

alpha-Lipoic acid (LA) has been intensely investigated as a therapeutic agent for several diseases, including hepatic disorder and diabetic polyneuropathy. However, the effects of LA or its reduced form, dihydrolipoic acid (DHLA), on cancer chemoprevention has never been reported. In the present study, we examined the effects of DHLA/LA on the production of nitric oxide (NO) by inducible NO synthase (iNOS) and the formation of prostaglandin E2 (PGE(2)) by cyclooxygenase-2 (COX-2), two important mediators associated with inflammation. DHLA/LA significantly inhibited lipopolysaccharide (LPS)-induced NO and PGE(2) formation in RAW 264.7 cells. Meanwhile, treatment with DHLA/LA suppressed the expression of iNOS protein but, unexpectedly, did not affect or increase the expression of COX-2 protein. The in vivo anti-inflammatory and antitumor-promoting activities were evaluated by a topical 12-O-tetradecanoylphorbol 13-acetate (TPA) application to mouse skin with measurement of edema formation, epidermal thickness and hydrogen peroxide production. DHLA significantly inhibited the priming and activation stages of skin inflammation induced by a double TPA application, by decreasing the inflammatory parameters. Furthermore, DHLA inhibited DMBA (0.3 micromol)/TPA (2.0 nmol)-induced skin tumor formation by reducing the tumor incidence and tumor multiplicity. When applied topically onto the shaven backs of mice prior to TPA, DHLA markedly inhibited the expression of iNOS protein. DHLA also strongly and directly inhibited COX-2 activity. These results suggest that DHLA can be a possible chemopreventive agent in inflammation-associated tumorigenesis.

Prevention of oxidant-induced cell death by lysosomotropic iron chelators

Intralysosomal iron powerfully synergizes oxidant-induced cellular damage. The iron chelator, desferrioxamine (DFO), protects cultured cells against oxidant challenge but pharmacologically effective concentrations of this drug cannot readily be achieved in vivo. DFO localizes almost exclusively within the lysosomes following endocytic uptake, suggesting that truly lysosomotropic chelators might be even more effective. We hypothesized that an amine derivative of alpha-lipoamide (LM), 5-[1,2] dithiolan-3-yl-pentanoic acid (2-dimethylamino-ethyl)-amide (alpha-lipoic acid-plus [LAP]; pKa = 8.0), would concentrate via proton trapping within lysosomes, and that the vicinal thiols of the reduced form of this agent would interact with intralysosomal iron, preventing oxidant-mediated cell damage. Using a thiol-reactive fluorochrome, we find that reduced LAP does accumulate within the lysosomes of cultured J774 cells. Furthermore, LAP is approximately 1000 and 5000 times more effective than LM and DFO, respectively, in protecting lysosomes against oxidant-induced rupture and in preventing ensuing apoptotic cell death. Suppression of lysosomal accumulation of LAP (by ammonium-mediated lysosomal alkalinization) blocks these protective effects. Electron paramagnetic resonance reveals that the intracellular generation of hydroxyl radical following addition of hydrogen peroxide to J774 cells is totally eliminated by pretreatment with either DFO (1 mM) or LAP (0.2 microM) whereas LM (200 microM) is much less effective.

Inhibition of LPS-induced nitric oxide and TNF-alpha production by alpha-lipoic acid in rat Kupffer cells and in RAW 264.7 murine macrophages

The activation of Kupffer cells represents a central mechanism of inflammatory liver injury involving the production of two important inflammatory mediators, nitric oxide and TNF-alpha. The aim of this study was to investigate the effect of the hepatoprotective compound alpha-lipoic acid (thioctic acid) on the production of nitric oxide and TNF-alpha in isolated rat Kupffer cells and RAW 264.7 macrophages. Isolated rat Kupffer cells or RAW 264.7 were either untreated, treated with alpha-lipoic acid (500 micro g/mL), or activated with 1 micro g/mL of lipopolysaccharide in the presence or absence of alpha-lipoic acid (0.2-500 micro g/mL). After 20 h the accumulation of nitrite was measured by the Griess assay. Tumour necrosis factor-alpha secretion was quantified after 4 h by L929 bioassay. Cell viability was determined by mitochondrial reduction of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) test, nuclear factor-kappaB (NF-kappaB) and activator protein-1 (AP-1) DNA binding activity by gelshift assays. Treatment of Kupffer cells and RAW 264.7 with alpha-lipoic acid alone had no effect on basal nitric oxide production. However, alpha-lipoic acid significantly inhibited lipopolysaccharide-induced nitrite accumulation. alpha-Lipoic acid did not alter basal TNF-alpha secretion in Kupffer cells, whereas it significantly inhibited lipopolysaccharide-induced TNF-alpha production. alpha-Lipoic acid attenuated the activation of nuclear factor-kappaB and AP-1, two transcription factors pivotal in induction of inducible nitric oxide synthase and TNF-alpha. alpha-Lipoic acid significantly inhibits lipopolysaccharide-induced macrophage production of nitric oxide and TNF-alpha via an attenuated activation of NF-kappaB and activator protein-1. The reduced production of nitric oxide and TNF-alpha in Kupffer cells may be involved in the hepatoprotective action conveyed by alpha-lipoic acid.

ESR and cell culture studies on free radical-scavenging and antioxidant activities of isoflavonoids

Isoflavonoids are thought to be the biologically active components in soy that play a role in the prevention of coronary heart disease and breast and prostate cancer. Mechanisms to explain how isoflavonoids mediate beneficial effects have not yet been clearly established. This study was undertaken to investigate the free radical-scavenging and antioxidant activities of various structure-related isoflavonoids including genistein, daidzein, biochanin A, and genistin in a cell-free and an endothelial cell model system. Electron spin resonance spectroscopy and spin trapping techniques were applied to evaluate the ability of isoflavonoids to scavenge hydroxyl, superoxide, nitric oxide, diphenylpicrylhydrazyl, galvinoxyl, and lipid-derived radicals. All isoflavonoids tested had no significant scavenging effects on the aforementioned radicals in concentrations up to 1.0 mM. However, at a physiologically achievable concentration of 5 nM, both genistein and daidzein slightly increased intracellular-reduced glutathione levels approximately by 10 and 30%, respectively, in human endothelial cells, whereas cellular alpha-tocopherol and uric acid remained unchanged by the isoflavonoid treatments. Present data indicate that free radical-scavenging activities of the isoflavonoids tested probably do not substantially contribute to their antioxidant properties. The ability of genistein and daidzein to increase cellular GSH (reduced glutathione) might be important for their action in biological system.

Antioxidant and prooxidant activities of alpha-lipoic acid and dihydrolipoic acid

Reactive oxygen (ROS) and nitrogen oxide (RNOS) species are produced as by-products of oxidative metabolism. A major function for ROS and RNOS is immunological host defense. Recent evidence indicate that ROS and RNOS may also function as signaling molecules. However, high levels of ROS and RNOS have been considered to potentially damage cellular macromolecules and have been implicated in the pathogenesis and progression of various chronic diseases. alpha-Lipoic acid and dihydrolipoic acid exhibit direct free radical scavenging properties and as a redox couple, with a low redox potential of -0.32 V, is a strong reductant. Several studies provided evidence that alpha-lipoic acid supplementation decreases oxidative stress and restores reduced levels of other antioxidants in vivo. However, there is also evidence indicating that alpha-lipoic acid and dihydrolipoic acid may exert prooxidant properties in vitro. alpha-Lipoic acid and dihydrolipoic acid were shown to promote the mitochondrial permeability transition in permeabilized hepatocytes and isolated rat liver mitochondria. Dihydrolipoic acid also stimulated superoxide anion production in rat liver mitochondria and submitochondrial particles. alpha-Lipoic acid was recently shown to stimulate glucose uptake into 3T3-L1 adipocytes by increasing intracellular oxidant levels and/or facilitating insulin receptor autophosphorylation presumably by oxidation of critical thiol groups present in the insulin receptor beta-subunit. Whether alpha-lipoic acid and/or dihydrolipoic acid-induced oxidative protein modifications contribute to their versatile effects observed in vivo warrants further investigation.

Uptake, recycling, and antioxidant actions of alpha-lipoic acid in endothelial cells

Alpha-lipoic acid, which becomes a powerful antioxidant in its reduced form, has been suggested as a dietary supplement to treat diseases associated with excessive oxidant stress. Because the vascular endothelium is dysfunctional in many of these conditions, we studied the uptake, reduction, and antioxidant effects of alpha-lipoic acid in cultured human endothelial cells (EA.hy926). Using a new assay for dihydrolipoic acid, we found that EA.hy926 cells rapidly take up and reduce alpha-lipoic acid to dihydrolipoic acid, most of which is released into the incubation medium. Nonetheless, the cells maintain dihydrolipoic acid following overnight culture, probably by recycling it from alpha-lipoic acid. Acute reduction of alpha-lipoic acid activates the pentose phosphate cycle and consumes nicotinamide adenine dinucleotide phosphate (NADPH). Lysates of EA.hy926 cells reduce alpha-lipoic acid using both NADPH and nicotinamide adenine dinucleotide (NADH) as electron donors, although NADPH-dependent reduction is about twice that due to NADH. NADPH-dependent alpha-lipoic acid reduction is mostly due to thioredoxin reductase. Pre-incubation of cells with alpha-lipoic acid increases their capacity to reduce extracellular ferricyanide, to recycle intracellular dehydroascorbic acid to ascorbate, to decrease reactive oxygen species generated by redox cycling of menadione, and to generate nitric oxide. These results show that alpha-lipoic acid enhances both the antioxidant defenses and the function of endothelial cells.

Lipoic acid confers protection against oxidative injury in non-neuronal and neuronal tissue

In the past decade or so, a convincing link between oxidative stress and degenerative conditions has been made and with the knowledge that oxidatiye changes may actually trigger deterioration in cell function, a great deal of energy has focussed on identifying agents which may have possible therapeutic value in combating oxidative changes. One agent which has received attention, because of its powerful antioxidative effects, particularly in neuronal tissue, is lipoic acid.